I believe the Casale parallel box you're talking about is what we ran in the old conventional hydroplanes back in the day as a "Z" drive. They had a 10 spline gear & I always wondered if they were the same as a 10 spline quick change gear but I never had both at the same time. Even if that is the case, (no pun intended) a new set of gears from Casale shouldn't be too expensive.
Sid.